It has long been known in the disposable absorbent bandage art that it is extremely desirable to construct absorptive devices, such as disposable diapers, sanitary napkins, incontinent devices, wound dressings, and the like, which are able to rapidly absorb discharged body fluids during high flow events, such as urination, without rapid spreading and leakage of the discharged fluids from the edges of the absorbent bandage structure. It is further recognized in the disposable absorbent bandage art that disposable absorbent bandage structures should present a dry surface feel to the user after the absorption process has been completed to improve wearing comfort and to minimize the development of undesirable skin conditions due to prolonged exposure to moisture.
Prior art web structures used as the wearer contacting surface on disposable bandages such as disposable diapers have been of two basic varieties, i.e., inherently fluid-pervious structures, such as fibrous nonwovens, and fluid-impervious materials such as polymeric webs which have been provided with a degree of fluid permeability via aperturing to permit fluid flow therethrough. Both varieties of prior art body contacting webs have been used in planar and in macroscopically expanded, three-dimensional configurations.
As utilized herein, the term "macroscopically expanded", when used to describe three-dimensional webs, ribbons and films, refers to webs, ribbons and films which have been caused to conform to the surface of a three-dimensional forming structure so that both surfaces thereof exhibit the three-dimensional pattern of said forming structure, said pattern being readily visible to the normal naked eye when the perpendicular distance between the viewer's eye and the plane of the web is not more than about 12 inches. Such macroscopically expanded webs, ribbons and films are typically caused to conform to the surface of said forming structures by embossing, i.e., when the forming structure exhibits a pattern comprised primarily of male projections, by debossing, i.e., when the forming structure exhibits a pattern comprised primarily of female capillary networks, or by extrusion of a resinous melt directly onto the surface of a forming structure of either type. Typically, it has been found that capillary networks having a maximum cross-sectional dimension of about 10 mils or more are visible to the normal naked eye at a perpendicular distance of about 12 inches. By way of contrast, the term "planar" , when utilized herein to describe webs, ribbons and films, refers to the overall condition of the web, ribbon or film when viewed by the naked eye on a macroscopic scale. In this context "planar" webs, ribbons and films may include webs, ribbons and films having fine scale surface aberrations on one or both sides, said surface aberrations not being readily visible to the naked eye when the perpendicular distance between the viewer's eye and the plane of the web is about 12 inches or greater.
Due to the relatively small size of the random interstitial openings formed by the entangled fibers or fibrous nonwoven webs, fibrous nonwoven topsheets are not always capable of rapidly transmitting dynamically deposited fluids to an underlying absorbent substrate, particularly in situations where the fluids deposited are quite viscous, e.g., menses, liquid bowel movement, etc. This can lead to unsightly accumulations on the wearer contacting surface of the topsheet and, in extreme cases, leakage of these materials from the edges of the bandage with resultant soiling of the wearer's outer garments. In addition, although it has been observed that prior art fibrous nonwoven topsheets are, in general, effective in removing static moisture from the wearer's skin, their fluid pervious nature normally permits reverse flow to occur under compressive loading, thereby causing rewetting of the skin by an underlying moist absorbent substrate. This rewetting tendency is particularly pronounced with the planar topsheet structures. Accordingly, prior art efforts to solve these problems have led to the development of embossed, three-dimensional, fibrous nonwoven topsheets.
One such embossed, three-dimensional, fibrous nonwoven topsheet structure is disclosed in commonly assigned U.S. Pat. No. 4,041,951 issued to Sanford on Aug. 16, 1977 and hereby incorporated herein by reference. The Sanford patent discloses a preferred disposable diaper structure comprising a moisture absorbent layer disposed between a soft topsheet and a moisture resistant backing sheet. The nonwoven fibrous topsheet preferably comprises an integral structure containing a multiplicity of depressed areas which intimately contact the uppermost surface of the moisture absorbent layer. The nondepressed areas of the topsheet contact the wearer's skin in use. In a particularly preferred embodiment, the nonwoven fibrous topsheet is comprised of a substantially non-wetting material exhibiting wet resilience such that the topsheet tends to resume its substantially three-dimensional character upon removal of pressure applied against the topsheet by the body movements of the wearer. The void space provided by the depressed areas taught by Sanford helps to reduce leakage of rapidly deposited fluids, from the edges of the diaper, while the physical separation provided by the three-dimensionally and wet resilience of such a topsheet helps to prevent direct contact between the moist absorbent core and the wearer's skin under most circumstances. Nonetheless, the fluid-pervious nature of the nonwoven material may permit some rewetting of the skin when compressive loads sufficient to substantially collapse the three-dimensionally of the topsheet are experienced in use.
Other attempts to deal with the rewetting problem have involved the use of topsheets comprised of fluid-impervious material provided with various forms of apertures. For example, U.S. Pat. No. 3,814,101 issued to Kozak on June 4, 1974, suggests a topsheet of non-fibrous, hydrophobic film which is provided with a plurality of valvular slits which allegedly restrict the reverse flow of liquid from the absorbent element of the device.
Commonly assigned U.S. Pat. No. 3,929,135 issued to Thompson on Dec. 30, 1975, and hereby incorporated herein by reference, suggests a macrosopically expanded, three-dimensional topsheet comprised of liquid-impermeable material, but provided with tapered capillaries, said capillaries having a base opening in the plane of the topsheet and an apex opening remote from the plane of the topsheet, said apex opening being in intimate contact with the absorbent pad utilized in the disposable absorbent bandage. Fluids deposited on the wearer contacting surface of the topsheet are freely transferred to the absorbent substrate, while flow in the reverse direction is inhibited by the decreasing cross-section of the tapered capillaries.
Still another material which has been utilized as a body contacting surface in a disposable absorbent bandage context is disclosed in commonly assigned U.S. Pat. No. 4,342,314 issued to Radel et al. on Aug. 3, 1982, and hereby incorporated herein by reference. The commonly assigned Radel et al. patent discloses an improved macroscopically expanded three-dimensional plastic web exhibiting a fine-scale three-dimensional microstructure comprising a regulated continuum of capillary networks originating in and extending from one surface of the web and terminating in the form of apertures in the opposite surface thereof. In a preferred embodiment, the capillary networks are of decreasing size in the direction of liquid transport. The web's fiber-like appearance is comprised of a continuum of fiber-like elements of substantially uniform U-shaped cross-section, each end of said fiber-like elements being interconnected to at least one other of said fiber-like elements. In a particularly preferred embodiment, the interconnected fiber-like elements are substantially nonaligned with respect to one another to enhance the fiber-like appearance.
While macroscopically expanded three-dimensional plastic webs of the type generally described in the aforementioned commonly assigned Thompson and Radel et al. patents have met with good success in permitting rapidly discharged body fluids, such as urine, to be transmitted from the surface on which they are initially deposited to an underlying absorbent core element with little or no leakage from the edges of the bandage structure, it has been observed that the wearer's skin may still look and feel moist upon removal of the bandage from the wearer's body. Since it can be quantitatively demonstrated that macroscopically expanded three-dimensional plastic webs of the type disclosed in the aforementioned patents to Thompson and Radel et al. are highly effective in preventing rewetting of the wearer's skin once discharged body fluids have passed into the underlying absorbent substrate, it is believed that much of the moisture remaining on the wearer's skin when absorbent structures employing topsheets of this type are removed from the wearer's body is not due to rewetting from the underlying moist absorbent core. Rather, it is believed that this fluid contacts the skin during the period or periods of high volume discharge and is simply never removed from the wearer's skin after the bulk of the fluid discharge has been transmitted to the absorbent substrate through the macroscopic cross-section capillary networks in the web. This is believed due to the low capillary suction exhibited by the macroscopic cross-section capillary networks in the web in relation to the relatively high capillary suction exhibited by the wearer's skin.
Accordingly, it is a principal object of the present invention to provide a macroscopically expanded, three-dimensional polymeric web with precisely controlled fluid transfer characteristics tailored not only to the fluid, but also to the range of flow conditions anticipated in use.
It is another object of the present invention to provide a macroscopically expanded, three-dimensional polymeric web which exhibits an ability to transmit rapidly deposited body fluid discharges through capillary networks of macroscopic cross-section to an underlying absorbent substrate, which is resistant to becoming co-planar under compressive loading, and which exhibits an ability to dry the wearer's skin of moisture remaining in contact with the skin once the bulk of the rapidly discharged fluid has been transmitted to the absorbent core of the structure.
It is another object of the present invention to provide such a web wherein the body contacting surface of the web in which the capillary networks of macroscopic cross-section originate is provided with a multiplicity of capillary networks which are substantially smaller in cross-section, said smaller capillary networks exhibiting sufficient capillary suction to transmit static fluid from moist objects which contact the surface of the web generally in the direction of an underlying absorbent substrate by capillary attraction.
It is still another object of the present invention to provide such a web, wherein said smaller capillary networks are oriented outwardly from the absorbent substrate to create a tortuous path which deposited liquids must follow to reach on edge of the absorbent device, thereby increasing the probability that the bulk of the deposited fluid will enter one or more of the large capillary networks before reaching the edge of the absorbent device.